check provenance attestation set in bake definition before overriding

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

test/attest/Dockerfile

@@ -0,0 +1,10 @@
+# syntax=docker/dockerfile:1
+
+FROM busybox AS t1
+RUN echo "Hello t1"
+
+FROM busybox AS t2
+RUN echo "Hello t2"
+
+FROM busybox AS t3
+RUN echo "Hello t3"

test/attest/docker-bake.hcl

@@ -0,0 +1,17 @@
+group "default" {
+  targets = ["t1", "t2", "t3"]
+}
+
+target "t1" {
+  target = "t1"
+}
+
+target "t2" {
+  target = "t2"
+  attest = ["type=provenance,mode=min"]
+}
+
+target "t3" {
+  target = "t3"
+  attest = ["type=sbom"]
+}